Commonly used minimally-invasive procedures for relieving stenoses, such as angioplasty or atherectomy, may dislodge plaque or blood clots. Once dislodged, such atheroma may be carried downstream by the blood and occlude smaller vessels, potentially cutting off the flow of blood to tissue. Such a blockage may present a serious risk to a patient's health, especially if the blockage occurs in a critical vessel leading to the heart or brain.
Moreover, procedures in which foreign objects are introduced into the bloodstream may cause the formation of clots. These clots, if released into the bloodstream, may also block the flow of blood, with potentially life-threatening consequences.
To reduce the risk of embolism, numerous previously known methods have been, and are being, developed. One previously known method, under development by Percusurge, Inc., Sunnyvale, Calif., involves temporarily blocking blood flow in an area in which a procedure is to be performed using a balloontipped occlusion catheter. Materials proximal of the blockage are evacuated from the vessel upon completion of the procedure, the occlusion catheter is removed, and the flow of blood is restored.
The foregoing method has serious drawbacks, however. For example, depending upon the vessel being occluded, the blood flow may only be blocked for a limited time before there is a risk of damage to tissue fed by the blocked vessel. Additionally, use of a balloon-tipped occlusion catheter to block flow may disrupt or loosen plaque within a vessel, much like an angioplasty balloon. This plaque may be released into the bloodstream after the balloon-tipped catheter is removed, possibly causing an embolism.
Another previously known method of reducing the risk of embolization uses a filter to catch loose plaque and clots, while permitting blood to pass through the filter. Numerous implantable filter devices have been developed to prevent clots from reaching critical areas, such as the heart or brain. These filter devices generally are removable only by surgery, especially if a filter device has remained in a vessel for an extended period, e.g., several weeks. Due to the difficulty with removing such devices, previously known filter devices generally are not appropriate for use with procedures such as angioplasty or atherectomy. Also, because these filter devices typically are constructed of a loose wire mesh, they filter out only large clots or plaque fragments.
For example, patients afflicted with chronic thrombophlebitis of the lower extremities often have recurrent pulmonary thromboembolism, which is treated by interruption of the vena cava with implantable filters. Because permanent obstruction of the vena cava can itself have detrimental effect on the patient's health, it would be desirable to provide implantable vascular filters that could be removed after a desired period of implantation.
Apart from implantable filter devices, a number of removable filter devices have been developed for short term use. These devices typically comprise a filter attached to a distal end of a device used during an angioplasty procedure. For example, U.S. Pat. No. 4,723,549, to Wholey et al. shows an angioplasty catheter having a filter disposed near its distal end; U.S. Pat. No. 5,160,342, to Reger et al. describes a guide wire having a filter disposed at its distal end. Such filter devices typically are kept in place only for the duration of a procedure, and are not appropriate for use over an extended period.
In view of the above, it would be desirable to provide a vascular filter device and catheter system that enable the vascular filter to be readily implanted and removed.
It would also be desirable to provide a vascular filter device that may be readily implanted within a vessel, remain in place for an extended period, and may be readily removed at the end of the period.